Means for controlling electric circuits



June 27, 1939. K. E. SCHIMKUS 2,163,709

MEANS FOR CONTROLLING ELECTRIC CIRCUITS Original Filed Jan. 30, 1935 vlimzrwwm/umm INVENTOR /Z A rZ/ Z56$Z227%Z1$.

- Patented June 27, 1939 UNITED STATES LIEAN S FOR CONTROLLING ELECTRICCIRCUITS Kurt a. Schimkus, Detroit, Mich, aesignor to Hannah 0.Chereton, Detroit, Mich.

Original application January 30, 1935, Serial No. 4,056. Divided andthis application December 15, 1937, Serial No. 179,893. Renewed October24 Claims. (01. zoo-113) The present application is based upon and is adivision of application, Serial Number 4,056, filed January 30, 1935,jointly by the present applicant and Willy Durnke, disclosing the samesubject matter disclosed herein and claiming subject matter not claimedherein.

The invention relates to devices for increasing and decreasing the flowof current in electric circuits and has as its general aim the provisionof a novel means which is simple, substantially free c i mechanicalnoise, practically indestructible from operative causes, and has nomoving parts requiring original or subsequent adjustment.

An object of the invention is to provide a novel device of the aboveclass which is capable of producing regular pulsations of current andoperates with low current loss and high efficiency.

Another object is to provide a device of this character which embodiesnovel means for effecting intermittent current pulsations through therecurrent conversion of a current conducting substance from one physicalstate in which it offers relatively little resistance to current flowinto another physical state in which current flow is substantiallyprevented and thereafter reconverting all or part of the substance toits original state.

A further object is to provide such a device which embodies means forefiecting cycles of current pulsations including a conductive materialcapable of changing its physical state in response to the application ofrelatively little heat energy arranged to be interposed in the circuitand confined in part to produce a predetermined re sistance to currentflow, whereby to generate heat energy ample to cause a change in thephysical state of said material at some point in the confined partthereof resulting in a break" of the circuit, the circuit beingpartially or entirely reestablishgl immediately thereafter by the returnof all or part of said material to its original physical state.

More specifically stated, an object of the invention resides in theprovision of a device arranged to be connected in a circuit andincluding, as a current conducting medium, mercury or mercury amalgam ina container which embodies a constriction, in the nature of a capillarytube, of such predetermined dimensions as will, when the deviceiscarrying the electrical energy for which it is intended, produce thatdegree of heat required to volatilize a small portion of the mer cury inthe constriction, whereupon the gaseous mercury interrupts thecontinuity of the metallic mercury and not only breaks the circuit butentirely stops or minimizes heat generation to permit condensation ofall or' part of the mercury vapor and partial or entire reestablishmentof the circuit.

In conjunction with the foregoing, another object is to provide a noveldevice embodying means which provides for the expansion and contractionof the mercury or other conducting medium under temperature changes,both internal and external, which means in dimensions is correlated withthose of the restricted tube to'insure proper operation.

Another object is to provide a device of this character which is notaffected by external shocks or vibrations and may be used in anyposition.

A further object is to provide a novel device in which failure of thedevice due to the introduction of extraneous matter, such as an air orgas bubble in the constricted portion of the conducting medium, is notpossible.

Stated more specifically, another object is to provide, a deviceembodying a mercury container having a restricted tube opening into asubstantially central point of the container, the quantity of mercury inthe container being less than the amount required to fillit and morethan that required to cover the end of the tube in all positions of thedevice and at the lowest temperature to which the device may besubjected.

Other objects and advantages will become apparent in the followingdescription and from the accompanying drawing, in which:

Figure 1 is a sectional view of a device embodying the features of theinvention.

Fig. 2 Ba similar view of such a device modifled in form for full-waveoperation.

Figs. 3 and 4 are wiring diagrams of circuits showing respectively themanner in which the devices illustrated in Figs. 1 and 2 may beconnected.

While the invention is susceptible of various modifications andalternative constructions, I have shown in the drawing and will hereindescribe in detail the preferred embodiment, but it is to be understoodthat I do not thereby intend to limit the invention to the specific formdisclosed, but intend to cover all modifications and alternativeconstructions falling within the spirit and scope of the invention asexpressed in the appended claims. v

Briefly stated, the features of the present invention are attained byutilizing the property of certain current conducting substances, ofwhich metallic mercury is an excellent example, to change the physicalcondition or state thereof, when subjected to heat, temporarily toanother physical state in which the substance is either non-conductiveor offers such high resistance to current flow as to be substantiallynon-conductive. With such a substance, and knowing in advance theaverage current values to be normally arranged to impart a.substantially fixed resistance to current flow of such value that theheat energy derived thereby will cause the conencountered by the device,the substance may be commercially as Pyrex.

version of a minute but sufficient quantity of said substance to itsnon-conductive condition to break the circuit and either entirelyinterrupt or decidedly decrease the current flow. Following the break,production of heat energy entirely or in large part ceases and thesubstance which has changed its physical state reverts entirely or insubstantial part to its original state and reestablishes the circuit.This constitutes one complete operating cycle. In operation the cyclicfrequency may be exceedingly high and is entirely independent ofmechanical or like limitations. Preferably the predetermined fixedresistance is obtained by forming the substance to provide a currentpath which is of predetermined dimensons,

The device thus functions to translate the direct current output of asource of electrical supply into a pulsating current, in which theactual current values vary at a predetermined frequency between maximumand minimum values. In certain instances, and depending upon theselection of the material which undergoes the change of state and alsodepending upon the electrical characteristics of the associated circuit,the current flow may be entirely interrupted at the conclusion of eachheating phase, and all of theconverted material may revert to itsoriginal state during the cooling phase. In other instances, the heatingphase may produce only a partial interruption of the current flow andthe cooling phase may result in only a partial reconversion of thematerial. In either event, however, the changes of state are accompaniedby and result in periodic variations of the ,current between welldefined maximum and minimum values, and in the illustrated embodimentsof the invention, these variations are abrupt and sharp. Throughout thefollowing description and in the appended claims, accordingly, termssuch as make, break, interrupt, recondense, reestablish, revert,reconversion, increase, decrease and the like are used in a generic andrelative sense. In the claims also, the term normal current is utilizedto refer to the increased value of current which flows through thesubstance at the conclusion of each cooling phase, or at the conclusionof each partial or entire reconversion' of the substance to its originalstate, which normal value of current again initiates the conversion oftltgetesubstance to its relatively non-conducting S Referring moreparticularly to the illustrative forms of structure shown in thedrawing, what may be termed a pulsator is shown in Fig. 1. Hereinaftermercuryor mercury amalgam (both being referred 'to in the followingdescription and in certain of the claims as mercurylwill be consideredas' exemplary of a suitable substance, the changes in the physicalstates thereof. being from a normal fluid state to a gaseous state,followed by condensation to the fluid state. The device shown in Fig. 1comprises two mercury containers HI which may be of any suitable sizeand shape but are preferably in the 'form of hollow substantiallyspherical members. These containers are spaced apart and are connectedby a tubular member I I having a bore l2 oppositely communicating withthe interior of each container. Where the device is intended to handleelectrical currents of relatively low value, the containers and the tubemay well be fashioned of glass, such as that known For higher values astronger material may be necessary.

The bore-is filled with mercury and the containers are nearly filled asshown, the mercury body being indicated at l3. 'Connection of the deviceis an electric circuit so that the mercury in the bore I2 is included inthe circuit and may be established by a terminal i4 sealed, as at IS, ineach container wall and contacting the body of mercury in eachcontainer.

Since in the transmission of electrical energy resistance is inverselyproportional to the size of the conductor, the fixed resistance of themercury may be advantageously predetermined and permanently maintainedby properly dimensioning the bore l2. For currents of low potential,such as. those drawn from a storage battery, the bore is quiterestricted and the tubular members may be in the nature of a capillarytube wherein the bore diameter is a fraction of a millimeter.

Moreover the length of the bore must be proper- ,ly calculatedapparently because of the fact that the mercury vapor produced when thechange of physical state occurs has substantially greater volume thanthe fluid mercury. In capillary tubes or like small diametered bores,the resistance to fluid flow therethrough is relatively great. Hence, ifthe bore is excessively long the gaseous mercury cannot readily overcomethe flow resistance offered with the result that the circuit may not bebroken or is not broken sharply and regularly. Conversely, if the boreis too short, expansion of the created gas may cause a greaterseparation of the mercury column than is necessary to break the circuit.In this case a permanent break in the circuit may result by failure ofthe broken ends of the column to reunite or an undesirable delay inclosing the circuit occurs due to the lag in the flow of the materialcaused by the resistance to flow. It is, therefore, desirable topredetermine the length of the bore to obtain that intermediate lengthwherein the circuit is broken sharply, regularly and in which therelationships are so balanced that substantially the initial conversionof mercury from the fluid to the gaseous state will break the circuit,immediately followed by a reconversion of gas to fluid which closes thebroken circuit. When the relationships are of this nature the device isexceedingly sensitive, will start at once upon closing the circuit andwill operate at a relatively high frequency,

Since the "break of'the mercury column is the result of change in thephysical state of mercury caused by the flow of electrical energy, theaverage values of the electrical current which is to be interrupted bythe device will determine the dimensions of the bore. Generally statedthe dimensions will increase as the values of the electricalcurrentincrease. As a particular example of dimensions which have beenfound satisfactory in a device for producing pulsating current from astorage battery in a circuit adapted to energize the primary winding ofa transformer, the restricted tube may have an approximate diameter oftwenty-two one-hundredths of a millimeter and a length of approximatelythree and eight-tenths centimeters.

Another factor to be considered is the quantity of mercury in thecontainers l0 since an opposing force is thereby imposed upon each endof the mercury column in the bore, which force will also affect thesensitivity of'the' device in operation. Consequently the quantity offluid in the containers will, if not held within predetermined maximumand minimum limits, have substantially the same effect as a bore l2which is too lon or too short. The quantity of fluid, in general,

ISO

increases as the,dimensions of the bore l2 increase. In the presentinstance the mercury in the containers l0 nearly but not quite fills.the containers, the bubblesof air or other gas IS in each containerbeing particularly provided to cury.

However, once the several factors to be taken into consideration areknown, it is not diflicult to determine the dimensional relationships ofthe several parts in the fluid confining system of a device intended foroperation in connection with current of a known average value. In thespecific illustration of container dimensions, a sphere of approximatelyone and nine-tenths centimeters has been found suitable in connectionwith a restricted tube of the dimensions above mentioned.

Unless, in a device of this character, some means is provided forpreventing the entrance of a bubble of extraneous gas, such as air, fromthe bubbles IS, the device can be used satisfactorily only in asubstantially horizontal position, due to the permanent interruption ofthe mercury column by the entrance of such a bubble. To this end thepresent invention preferably embodies means whereby no foreign matter ofany kind can enter and become lodged in the bore l2 which arrangement isbeing claimed in said joint application, Serial-No. 4,056. Thus. asshown, each end of the tubular member H is extended through the wall ofthe associated container Hi to a point which is substantially centrallythereof so that the ends of the bore are located approximately on thecenter points of the containers. The ends of the tubular member II arepreferably rounded, as indicated at H, to avoid trapping air bubbles onthe ends, as the mercury is introduced into the containers through thefilling openings, shown in sealed condition at l8. With this arrangementof parts.-

and with the containers properly dimensioned. the quantity of mercury inthe containers will be more than ample to cover the exposed ends of thebore l2 regardless of the position of the device. Hence, air bubbles, orindeed any foreign matter, such as minute particles of oxide of mercury,cannot possibly enter the bore.

It has been found that theunion between the tubular member and eachcontainer is stronger and the mercury is better supported if the wallportions of the containers about the tubular member are turned inwardly,asshown, to form a smooth junction. Moreover, to lessen electricalresistance externally of the born I! the terminals l4 are extended topoints immediately adjacent to the bore ends. v

The device shown in Fig. 1 is intended primarily to be used forcontrolling the simplest type of circuit, such as a circuit foreffecting energization of a transformer by a pulsating current. In Fig.2 a device is shown for controlling a circuit which includes twobranches, such as a circuit by which energization of a transformer bycurrent alternating in direction is effected. The construction of thelatter device, as well as the correlation and relationship of the partsthereof, is substantially the sameas that shown in Fig. l, as isindicated by the use of the same reference numerals. However, in thisform, the tubular member I l is interrupted between its ends and theinterrupted ends communicate with opposite sides of an intermediatecontact chamber IS. The casing forming this chamber is preferablysmaller than the containers l 0 and is filled with mercury. At one sidea terminal 20 extends through the casing wall to a point intermediatethe opposed ends of the interrupted bore l2. In this device theoperation is the same as in the first device except that two restrictedbores are provided for controlling the branch circuits.

Since it is practically impossible to balance the bore branches exactly,the initial breaking of thecircuit will occur in one or the other of thebores, after which the circuit through the other bore will be brokenwhile the first circuit is being reestablished. Consequently this formof device will be effective to make" and "break branch circuits inalternation.

In illustration of circuits embodying these devices and in descriptionof an environment in which these devices have been found particularlysuitable, Figs. 3 and 4 show circuits employed in converting low voltagedirect current from a storage battery into high voltage direct currentfor supplying the "B circuit of a radio receiving set with currenthaving a proper potential. Such circuits are used largely in theso-called B battery eliminator devices employed in motor vehicleinstallations of radio receiving sets.

Fig. 3 shows the device in the capacity of a pulsator. Thus, oneterminal I4' is connected through lead 2! with one side of a storagebattery 22 which in turn is connected by lead 23 and interposed controlswitch 24' with one end of the primary winding 25 of a step-uptransformer 26.

The other end of the primary winding is connected by lead 21 with theother terminal M. This circuit is effective to energize the primarywinding intermittently and always in the same direction, which pulsatingcurrent is, however, reflected as an alternating current in thetransformer secondary winding. A condenser 28 is connected across thedevice by leads 29 to the leads 2| and 21' and serves to tune thecircuit and reduce the slight electrical noise resulting from r theoperation of the device. The condenser 28 also appears to affect orcontrol the frequency of the device.

To complete the circuit any suitable means for rectifying the currentfrom the secondary winding 30 may be employed, such as a thermionicvalve 32. Herein one end of the secondary winding is connected by lead3| with the plate element 33 of such a valve. while the cathode element34 is connected with an output lead 35 to one side of a suitable filtersystem, generally designated 36. The other end of the secondary windingis connected by lead 31 with the other side of said system. A condenser38 may be connected by leads 38a. across the leads 3| and 31 from thesecondary winding. The valve has a heating filament 39 connected byleads 39a directly with the battery 22, although the switch 24 'isinterposed.

In operation, closing of the switch 24 produces a current flow throughthe interrupting device,

the resistance to which flow almost instantly heats the mercury in thebore and causes a small part of the mercury to volatilize. This changeof state through the increased volume occupied by l the gas breaks"'thecircuit and immediately thereafter condensation of the gas reestablishesthe circuit. Repetition of this cycle of operation at ahigh frequency iseflective to energize the primary winding intermittently and produce analternating current of high voltage in the secondary winding which isrectified to an intermittent direct current by the valve 32, andsmoothed into a substantially even direct current by the filter systemfor delivery to the proper terminals of a radio receiving set.

With the circuit shown in Fig. 4 energy from a storage battery istranslated into pulsating components successively opposite in direction.Thus, the end terminals l4 from the device are connected through leads40 with the ends of primary winding 4|, condensers 42 of proper valuebeing connected in series across the leads 40 by leads 43. Theintermediate or third terminal 20 of the device is connected by lead 44with the lead 43 between condensers 42 and with a control switch 45which, in turn, is connected with one side of the battery 46, the otherside of which is connected with-an intermediate or center tap 41 fromthe primary winding. Each end of the secondary winding 48 is, in thissystem, connected through a lead 49 with a plate element 50 of athermionic valve 5| of the full-wave type. A cathode element 52cooperatively related to said plate elements is connected with an outputlead 53 to a suitable filter system which may be of the type shown inFig. 3 and is generally represented by the first condenser. A heatingfilament 54 is connected independently with a battery through leads 55and a condenser 56 is connected across the secondary winding by leads51.

- The operation of this system is substantially the same as that of thecircuit illustrated in Fig. 3. However, in this system the alternate"making and breaking of the circuits in the opposite branches of thebore is eflective to energize first one and then the other section ofthe primary winding, the current flow being in opposite directions.'Prope'r adjustment of the values of the condensers 42 may be employedto synchronize the current pulsations in the two branches of the bores.The resulting alternating current induced in the secondary winding isrectified, filtered and substantially direct current of high po tentialis delivered to the receiving set. This system is probably moreefficient than the first described system.

From the foregoing it will be evident that a. novel circuit controllingmeans has been provided which is unusually simple in construction. Thedevice occupies a closed container. Hence the substance therein is notsubject to oxidation or other chemical changes and will remain in itsoriginal condition indefinitely. The device is efiicient since the onlycurrent loss is the result of the relativelylow resistance oiiered bythe substance imposed in the circuit. The only change caused by thecurrent fiow is one of physical state and the substance, therefore, isnot expended or in any manner aifected deleteriously by operation. aThere are no moving parts in the present device, hence accurateadjustment is not required. Upon determination of the proper correlationof dimensions and quantity of substance for a current of average valuesquantity production-of uniform devices may be easily obtained. Inaddition, the device may be used in any position and. under practicallyall operating conditions without injury thereto or impaired performance.As a result of these several advantageous features devices embodying thepresent invention are exceedingly practical, eflicient, adaptable formany uses and may be economically manufactured.

What is claimed is:

1. In a device for rapidly and recurrently increasing and decreasingcurrent flow in a circuit having a substantially constant voltageapplied thereto, the combination of means providing a passageway,current conducting material filling said passageway to provide aconductor for current, saidmaterial having the property of changing itsphysical state when heated to a state in which the material is asubstantial. non-conductor of the'current subjected thereto, saidpassageway being dimensioned so that the normal quantity of currentfiowing therethrough produces heat energy sufiicient for causing saidchange of physical state, and means for connecting said material in thecircuit. a

2. In a device for rapidly and recurrently increasing and decreasingcurrent flow in a circuit, the combination of means defining a bore,fluid material filling said bore and having the property of being a goodcurrent conductor when in a fluid state and a poor current conductorwhen in a gaseous state, said bore being dimensioned according to theaverage values of electrical energy to be impressed upon the device sothat the normal current through the material causes the production ofheat energy sufiicient to change a part of said material insaid borefrom its fluid to its gaseous ,state whereby to reduce the flow ofcurrent through said material, and means for establishing said materialin the circuit.

3. In a device for rapidly and recurrently increasing and decreasingcurrent flow in a circuit, the combination of means defining a bore,fluid material filling said bore and having the property of being a goodcurrent conductor when in a fluid state and a poor current conductorwhen in a gaseous state, said bore having a length and cross sectionalarea predetermined according to the normal value of the electricalcurrent to be passed through the device so that said normal currentheats'said material to a point where a physical change of a portionthereof within said bore to a gaseous-state occurs to reduce the currentflow until condensation within said bore of the gaseous materialreestablishes at least in substantial part the original conductivity ofthe material, and electrical connections to said material.

4. In a device for rapidly and recurrently increasing and decreasingcurrent flow in a circuit, the combination of means defining a bore,mercury in said bore, and means for passing electric current throughsaid mercury, said bore being dimensioned so that normal current flowproduces heat energy sufiicient to heat a small portion of saidmercurywithin the bore to a point where vaporization of said portionoccurs to sharply reduce the conducting continuity of the mercury.

5. A device for rapidly and recurrently increasing and decreasingcurrent flow in a circmt comprising the combination of a restricted tubeconmercury in the circuit, the normal flow of cur-' rent beings'uflicient' to heat the mercury to its transition point and sharplyreduce the current fiow in the circuit, and means permitting theexpansion and contraction of the mercury without affecting the circuit.

7.,In a device for rapidly and recurrently increasing and decreasingcurrent fiow in a circuit, the combination of means providing apassageway, current conducting material filling said passageway of acharacter that applied heat causes a change of physical state to asubstantial nonconductor of current, and means for connecting saidmaterial in said circuit, said passageway having dimensionspredetermined according to the normal value of the current passingthrough said circuit so that said normal current produces the quantityof heat necessary to cause such change of physical state of a part ofthe material in said passageway.

8. In a device for rapidly and recurrently increasing and decreasing thenow of electrical energy in a circuit, the combination of a substancewhich is current conducting in one physidakstate and substantiallynon-conducting in another physical state, the transition from one stateto the other being produced by heating or cooling, and means forconnecting in a circuit having a predetermined normal current flow saidsubstance'in such quantity that the normal current flow produces heatenergy just sufiicient to cause a change of physical state to asubstantially non-conducting condition whereupon the subsequentimmediate cooling changed substance at least in part to its originalstate, to thereby entirely or in substantial part reestablish theoriginal conductivity of the circuit.

9. A device for rapidly and recurrently increasing and decreasingcurrent flow in a circuit coinprising, in combination, a tube having apassage therethrough of restricted size, a hollow container at each endof said 'tube, said tube being filled and said containers partiallyfilled with mercury to maintain an unbroken continuity of mercury insaid tube, said tube being dimensioned to produce the heat energyrequiredwhen a normal current passes through the mercury column thereinto interrupt the liquid continuity thereof, said containers being filledwith mercuryto the extent that upon such interruption the increasedpressure in the containers causes the interrupted portions of themercury column to be substantially instantly rejoined, and electricalconnections with the mercury in said containers.

10. In a device increasing and decreasing at high frequency the currentfiow in a circuit, the combination of means defining a restricted borehaving mercury therein, said bore being dimensioned so that the mercurycolumn is incapable of carrying the normal quantity of current flow andis broken along its length by the action of such normal current, andmeans providing a confined gas space communicating with said bore toprovide pressure for at least in large part re- .establishing the broken-mercury column, the

pressure exerted being predetermined to permit the merciu'y column tobreak instantly and to eflect a subsequent substantially instant saidreestablishment of the broken colummand means returns the container andpartially filling the end containers, and means on each container forestablishing electrical connections with said body of mercury.

12. A device of the class described comprising, in combination, anelongated tube having a container at each end, a body of mercury fillingsaid tube and partially filling each container to leave a space thereinoccupied by a compressible fluid, and means for establishing anelectrical circuit from one container to the other through said tube,said tube being dimensioned so that the normal flow of currenttherethrough will eifect an interruption of the liquid continuity of themercury body, the compressible fluid in said containers having abalanced relation to exert approximately equal forces on each side ofthe interruption and in oppositon to the interrupting force to effectsubstantially instant substantial remaking of the-continuity of themercury body after each interruption.

13. In a device for rapidly and recurrently increasing and decreasingcurrent fiow. in a circuit, the combination of means providing apassageway, current conductlng material filling said passageway of acharacter that applied heat causes a change of physical state to asubstantial nonconductor .of current, means for connecting said materialin said circuit, said passageway having dimensions predeterminedaccording to the normal value of the current passing through saidcircuit so that said normal current produces the quantity of heatnecessary to cause such change of physical state of a part of saidmaterial in said passageway, and means for subjecting said part of saidmaterial to a pressure tending to cause said part of said material toresume its conductingstate within said passageway.

, 14. In a device for rapidly and recurrently increasing and decreasingcurrent flow in a circuit, the combination of means defining a bore,fiuid material filling said bore and having the property of being a goodcurrent conductor when in a fiuid state and a poor current conductorwhen in a gaseous state, said bore having dimensions predeterminedaccording to the normal values oi. the electrical current to be passedthrough the device so that said normal current is capable of heatingsaid material within the bore to a point where a physical change of aportion thereof within said bore to a gaseous state occurs to reduce thecurrent flow until condensation within the bore of the gaseous materialentirely or in substantial part reestablishes the circuit,,means forsubjecting said material to a pressure tending to cause saidcondensation andreestablishment, and electrical connections to saidmaterial.

15. In a device for rapidly and recurrently increasing and decreasingcurrent flow in a circuit, the combination of means defining a bore,mercury in said bore, means for passing electric current through saidmercury, said bore being dimensioned so that the normal current fiowthrough said mercury in the bore produces heat energy suiilcient to heata small portion of said mercury in said bore to a point wherevaporization occurs to break the liquid continuity-of the mercury, andmeans for-subjecting said mercury to a pressure tending to cause saidvaporized mercury to recondense within said bore and reestablish saidcontinuity.

16. A device of the class described for connection to points ofdifferent potential comprising, in combination, a tube having arestricted bore therein interrupted intermediate its ends by an enlargedchamber, closed containers at the ends of said tube in communicationwith said bore,

mercury in said containers and filling said bore and chamber, a terminalindivdual to each end of the tube, a terminal for the chamber anddimensions predetermined according to the nor-- mal value of the currentpassing through said circuit so that said normal current produces thequantity of heat necessary to cause such change of physical state of apart of the material in said passageways, means for connecting thematerial at one end of each passageway to one of said points, and meansfor connecting the material at the other end of each passageway to theother of said points.

18. In a device of the'class described for connection to points ofdifferent potential, the com-.- bination of means providing a pair ofpassageways communicating with each other at a junction thereof, currentconducting material in such passageways of a character that applied heatcauses a change of physical state to a substantial nonconductor ofcurrent, said passageways having dimensions predetermined according tothe nor mal value of the current passing therethrough so that saidnormal current produces the quantity of heat necessary to cause suchchange of physical state, means for connecting the ends of saidpassageways to one of said points, and means for connecting saidjunction to the other of said points.

19. In a device of the class described for connection to points ofdifierent potential, the combination of means providing a pair ofpassageways communicating with each other at a junction'thereof, currentconducting material in such passageways of a character that applied heatcauses .a change of physical state to a non-conductor of current, saidpassageways having di. mensions predetermined according to the normalvalue of the current passing therethrough so that said normal currentproduces the quantity of heat necessary to cause such change of physicalstate, and means for connecting said material to said points.

20. In a device for rapidly and recurrently increasing and decreasingcurrent flow in a circuit, the combination of means defining a bore,fluid material filling said bore and having the property of being a goodcurrent conductor when in a fluid state and a poor current conductorwhen in a gaseous state, said bore having a length and crosssectionalarea predetermined according to the normal value of the current to bepassed through the device so that said current is capable of heatingsaid material to a point where a physical change of a portion thereofintermediate the ends of said bore to a gaseous state occurs to reducethe current flow, said gaseous material recondensing at least in partupon the reduction in current fiow thereby increasing the conductivityaction, and electrical connections to said material.

21. In a device for rapidly and recurrently increasing and decreasingcurrent flow in a circuit, the combination of means defining a bore,liquid mercury in said bore, and means for passing electric currentthrough said mercury, said bore being dimensioned according to thenormal current passed through said mercury so that said normal currentproduces heat energy sufficient to heat a small portion of said mercurywithin said bore to a point where vaporization occurs to break theconducting continuity of the liquid mercury, said vaporized mercurybeing at least part recondensed within said bore upon said break so asto at least partially restore the original conducting continuity of themercury. 1

.22. In a device for rapidly and recurrently in creasing and decreasingcurrent flow in a circuit, the combination of means providing apassageway, material filling said passageway which in one state is agood conductor and in a second state is a relatively poor conductor,said material being adapted to pass from said one state to said secondstate upon the application of heat, means for connecting said materialin said circuit, said passageway having dimensions predeterminedaccording to the normal value of the current passing through saidcircuit-so that said normal current produces the quantity of heatnecessary to cause said change in state of at least a part of thematerial in said passageway, and means for j applying pressure to saidmaterial in said passageway so as to confine said part of said materialto said passageway and so as to tend to cause said part of said materialto revert to said one state.

23. In a device for rapidly and recurrently increasing and decreasingcurrent flow in a circuit, the combination of means defining a bore,fluid material filling said bore having the prop-- erty of. being a goodconductor when in a fluid state, and a poor conductor when in a gaseousstate, said bore being dimensioned according to the normal value of thecurrent to be passed through the device so that said normal current iscapable of heating said material to a point where I a physical change ofa part thereof intermediate the ends of said bore to a gaseous stateoccurs to reduce the current fiow, and means for applying pressure tothe material in said bore so as to confine said gaseous part within saidbore and so as to promote recondensation of said gaseous portion.

24. In a device for rapidly and recurrently increasing and decreasingcurrent flow in a circuit, the combination of means defining a bore,fluid material filling said bore having the property of being a goodconductor when in a fluid state, and a poor conductor when in a gaseousstate, said bore being dimensioned according to the normal value of thecurrent to be passed through the device so that said normal current iscapable of heating said material to a point where a physical change of apart thereof intermediate the ends of said bore to a gaseous stateoccurs to reduce the current flow, and" means for applying pressure tosaid material so that said gaseous part occupies only a small proportionof the length of said bore and so as to promote recondensation of saidgaseous portion.

KURT E. SCHIMKUS.

